Maybe a better bet is to get two 12Vs and connect in series. I am running a course on electrics for wind turbines starting on the 17th Nov 2009, and there will probably be a few people who want to buy batteries. If we collect these orders together we may be able to negotiate a good price. If you plan to come to the course, we can talk then, otherwise if you are not in a big hurry contact me after the 17th and we will see how many people want to order.

My turbine is churning out amps and my PV panels are churning out amps and the time has come to look deeply at my battery situation.

I have two second-hand golf-cart batteries and two 172ah second-hand Telkom batteries or about half a ton of batteries but effectively I don't have much at all. They charge too quickly and they discharge too quickly.

So I contacted my son who is a mechanical engineer in the USA and he writes technical articles for aero magazines and owns his own aeroplane. He knows the technical writing fraternity and he asked around if anyone had a way to rescue a battery. Well he got a couple of replies most very technical and of no use to me but here's one and I quote :

Subject: Bringing Batteries Back from the (almost) DeadFound on another list...it works BTW, I`ve tried it. Marc

I didn`t believe this would work but as luck would have it, I had flownto Reno with the bad battery, visiting family, when a long technicalthread came on line. The trick is to pass a constant charging current ofl to 2 amps thru the battery for many hours. Mine took 3 days before thespecific gravity stopped rising.

Get a 3 AMP x 200 volt or higher diode (Radio Shack $0.75). Cut 1 wireof an extension cord and connect one cut end to the negative batteryterminal. Connect BAR marked end of the diode to the battery (+)terminal (the arrow will now point toward the battery). Connect theother end of the diode to the other cut end of the extension cord.

Plug in lamps to the extension cord. You will get .63 amps per 150 wattbulb so 2 bulbs are faster. Tape or protect your connections and plug into 120 VAC. Wait as long as you can. You cannot overcharge and this willwork from 2 volts to 28 volts since it is current regulated.

[Note that he`s recommending wiring the lamps and the battery in SERIES;if you put even rectified 110 volts across a lead acid battery, you`llsoon have a hydrogen explosion combined with sulfuric acid spray. Very,very bad thing. Paul]

Unquote

The article is a bit disjointed but I've put together a piece of apparatus (see picture) which consists of a fan, a bridge rectifier and eight kettle elements. I intend to rectify the mains current and then put it through a suitable configuration of kettle elements and then charge one golf-cart battery at 1 amp for as long as it takes. I have an SG meter and I'll monitor and record my readings and time as I go along. I'll let you know how I fare.

This is bowls-speak for losing along with we came second or "It's not all about winning" etc etc but in this case I did indeed have a success and some failures.

Success. My apparatus is up and working - whether it will now go on to rescue batteries we shall still see.

Failure. A guy gave me an SG meter years ago and I unearthed it in my deepest box and it is finito. The rubber nozzle and the rubber bellows are kaput. All efforts at ressurection failed and in this little town it's not possible to buy one. No SG readings !!!!

Failure. My calculations regarding how many kettle elements would do the trick. I wired in 3 in series and then in series with 2 in parallel. Finally we found the right formula by trial and error. It took 8 elements in series. A basic misunderstanding was that I measured the rms voltage of the output of the bridge rectifier which gave 94.5 V. That's a rubbish measure in this case because when you measure it as DC you get 204 V. I based my calcs on the lower value. Quite frankly even the DC value is "wrong" because when you calculate the voltage difference over the battery you get 10 V which is obviously wrong because measuring DC across the battery you get 13.5 V and that's because the battery is "seeing" those positive peaks that exceed the battery voltage. It finally took an ammeter in circuit and adding elements till we got 1.3 amps into the battery. So much for being "clever".

Failure. My estimation of how hot the elements would get and how much current the whole arrangement would take. I thought 1.3 amp through 23 ohm resistance W = I squared R or 38.87 W per element and when you use it to boil water you use 2000W or one fiftieth of the normal heat. Not so - it gets too hot too touch - granted in the normal situation it would have glowed red hot in the air. Anyway it was fortunate that I had included a fan - it was necessary. I budgeted on 4 elements (equivalent) which at 1 amp would have taken about 150 W - well now it is taking over 300 W.

Overall it was a success !!!!! That is the practical reality - the rest was an ego trip.

I started wiring the @#$#@# thing in my lounge thinking I'd move it later but when it actually started working we let it do it's thing and it can carry on all night. My life's a mess and tomorrow that apparatus goes out of my lounge. Anyway the pictures show it all working IN MY LOUNGE !!

I'll get an SG meter and I'll perform the next "rescue" under more controlled conditions. We shall see what we shall see.

I've now put in a transformer from 230V to 30V and adjusted the load till the battery receives just over 1 amp. It will save me a lot of money !!

In any case the red battery is OK. After charging at 1.3 amps for 24 hours all the cells are giving off bubbles. To begin with only 3 did. I believe trickle charging has a role to play.

Now the big test. Will my golf-cart batteries respond to the same treatment ?? I would have already started but I'm waiting for the SG meter I've ordered from Mossel Bay with the courier - amazingly Auto-Zone doesn't charge for that service - and when it arrives I'll get a basic reading on each cell. Then it's off to the races !!!!!

If my golf-cart batteries respond then OK, if not then .........

....... I'll re-visit all the info my son has sent me and try another strategy. Hopefully by the time I either rescue or destroy my batteries I will have learnt enough about lead-acid batteries to be able to appreciate the new ones I'll then have to buy (maybe) and know how to treat them.

Incidentally I read in the papers today there may very well be a shortage of rare-earth metals soon. Maybe we'll need the good old lead-acid batteries a bit longer and this knowledge won't be all wasted. Who knows ????

My two second-hand golfcart batteries were not performing and so armed with my now efficient trickle-charger and hydrometer I took the challenge.

First I turfed out all the old acid and re-filled with new battery acid. First lesson, battery acid besides being dangerous is very expensive. I expected the dangerous part so I got out my trusty rubber gloves and protective goggles but was unprepared for the price. The spares shop offered me R35 / liter !!! Golfcart batteries take nearly four liters or some R140. This was not a good start.

Anyway I got the new acid in and measured the SG (Specific Gravity) - way into the red on all cells !!! OK, so I connected the trickle-charger and monitored it for a solid week. The SG never came into the green for any cell but two cells eventually got to white (fine), the rest remained firmly in the red. The voltage crept up from 12V to 13.3V but sagged back to 12.3V about four hours after disconnecting.

I was not pleased. R140 plus a week's charging current for such marginal improvement was not exactly my idea of success. I've kept the battery because I need two batteries for my two computer UPSs and another for my solar PV panels - I keep my two Telkom batteries for the 24V wind turbine. I'm doing the same to the other golfcart battery at this time - only difference is that this time it is charging in the garage and not in my lounge !!!

My opinion, for what it's worth, is that once a battery is finished it is finished and requires replacement. Rejuvenation, resurrection or rescuing is not going to yield economically viable results. It appears to me that when the technician at the golf course establishes the battery won't serve their purposes any longer then it won't for us non-professionals either. The batteries pass the ordinary car soak test tester and that is the best we can bring to bear on the problem (it will identify badly shorted cells and prove that it could start a car !!??) but it is not sufficient to prove that the battery will be capable of delivering the goods under pressure. In fact, these batteries can and do run banks of LED lights (Big Deal !!!) and back up the computer UPSs (I threw out the small 12 V batteries that come with them) so are not entirely useless but don't try and power an inverter and run anything substantial, for instance a computer never mind a fridge, for any useful duration.

In future I'm going to invest in brand new batteries no matter what, this agony and expense is too great.

As I understand it, it all depends on how bad the batteries are. A battery that has been allowed to stand discharged for a while, will form crystals on the lead. This is called sulphation. A solid layer of crystals means the end of the battery - nothing will shift them. If you take the battery apart you can see a white layer over the lead. It might be possible to physically scrape this off.

If there is alight sulphation, then some special chargers use a pulse of high voltage which 'blasts' the sulphation off the lead, exposing the metal, which can then react with the acid again.

The problem with pouring out the acid and replacing it, is you don't know how much of the sulphur is on the plates. So the concentration might be wrong in the end.

So just because it didn't work on those batteries, doesn't mean your system won't work on all batteries. But basically I agree with you - the cost saving is not worth it, so buying new batteries is probably worth it.

I've just worked myself up about my golfcart batteries and then I have a huge success. Things are so unpredictable !!

Anyway I went through the routine of changing the battery acid and then stuck the battery on the trickle charger (the second golfcart battery) and forgot about it for more than a week. Today I went and measured the SG and 2 cells were in the green, 3 in the white and 1 just in the red. The voltage was 13.8 and the batteries were bubbling happily. This battery looks real good. Very likely nowhere near 100% because most of the cells never reached green but it should be around 50% and that will mean that's it's the best battery that I've had.

Tomorrow I will move it into the house and put the LED lights on it. This may not sound significant but to me it will be an "acid" test so to speak. I bought a meter long LED strip (daylight) from Windgat and left them permanently on with my computer UPS charging the battery (one of my big Telkom batteries) and about two weeks later I measured the voltage of the battery ??!!! I expected the voltage to be over 13 V but to my horror it was 12.2V !!! So to say flat - WOW ???

The consumption of those LEDs must exceed the charging rate of the UPS. Either these LEDs take more than what I thought or the charger on the UPS is pathetic or my battery is giving up the ghost. I'll establish what happened and let you know. Still I'm hoping that this second golfcart battery can perform under fire, so to speak.

My estimation of how hot the elements would get and how much current the whole arrangement would take. I thought 1.3 amp through 23 ohm resistance W = I squared R or 38.87 W per element and when you use it to boil water you use 2000W or one fiftieth of the normal heat. Not so - it gets too hot too touch - granted in the normal situation it would have glowed red hot in the air. Anyway it was fortunate that I had included a fan - it was necessary.